1. Field of the Invention
The present invention relates to image writing devices and methods for reproducing electronic images, and more specifically to image writing devices and methods that are less costly to implement and faster than heretofore known imagc forming devices.
2. Description of the Related Art
In image forming apparatuses of the electrophotographic type such as page printers, digital copying machines and the like, print heads of the mechanical scanning type which scan (a "main scan") by deflecting a laser beam via a polygonal mirror are widely used as an image writing means, wherein a photosensitive member is at least partially optically exposed in accordance with image information.
Multibeam scanning, wherein a plurality of laser beams arc used to simultaneously scan a plurality of lines, is effective in shortening the time required to expose a single image surface by laser beam. For example, if two lines are scanned simultaneously, the time required for exposure is theoretically 1/2 the time required when scanning one line at a time.
In multibeam scanning, however, wherein a plurality of adjacent lines are simultaneously scanned, there is a limit to the reduction in line pitch due to restrictions in the dimensions of the light source. That is, it is difficult to attain high resolution.
Heretofore, methods have been proposed for simultaneously scanning a plurality of lines at set line intervals of a constant number of lines (Japanese Unexamined Patent Application No. SHO 56-110960).
In image forming apparatuses such as page printers and the like, an image is hypothetically drawn on an image memory prior to exposure scan. Thus, image data (bitmap data) in pixel units expressing an image are transmitted from image memory to the control unit of the laser light source for each exposure scan, so as to modulate the laser beam in accordance with said image data.
When scanning is accomplished by a single laser beam, image data may be sequentially transmitted from the image memory to the control unit one line at a time from the first line.
When simultaneously scanning M lines at a constant line interval, however, suitable scanning cannot be accomplished only by transmitting image data sequentially from the first line. The above-identified Japanese patent application did not specifically address a suitable method for transferring image data.
There thus exists a need for an image writing device and method that is capable of providing for simultaneous transfer of image data when using multibeam scanning. Moreover, there is a need for an image writing device and method that can accomplish high speed simultaneous transfer of image data at relatively low cost.